Recently, a large number of semiconductor lasers (laser diodes) have been used as signal light sources or excitation light sources of optical fiber amplifiers in optical communications. When a semiconductor laser is used as a signal light source or an excitation light source in optical communications, it is mostly used as a semiconductor laser module in which a laser light from the semiconductor laser is optically coupled to an optical fiber.
FIG. 7 shows a schematic cross-sectional view of one structural example of a semiconductor laser module. The semiconductor laser module 1 is obtained by placing a semiconductor laser element 2 and an optical fiber 3 in an optical coupling state and by accommodating and arranging them inside a package 4.
In this semiconductor laser module 1, a temperature control module (peltier module) 5 is fastened inside the package 4. A metallic base 6 is fastened on the temperature control module 5. The semiconductor laser element 2 is fastened above the top face of the base 6 via an LD carrier 7. A photo diode 9 is fastened via a PD carrier 8. A thermistor (not shown) is arranged near the semiconductor laser element 2.
The photo diode 9 monitors a light emitting state of the semiconductor laser element 2, and the temperature control module 5 controls the temperature of the semiconductor laser element 2. The operation of this temperature control module 5 is controlled based on the temperature detected by the thermistor so that the semiconductor laser element 2 is kept at a constant temperature. By the temperature control of the semiconductor laser element 2 performed by the temperature control module 5, the intensity variation and the wavelength variation of the laser light of the semiconductor element 2, which results from the variation in temperature of the semiconductor laser element 2, are suppressed. This enables the intensity and the wavelength of the laser light from the semiconductor laser element 2 to be kept almost constant.
Furthermore, a ferrule 11 is fastened to the base 6 by a fastening member 17. The ferrule 11 is made of metal, such as Fe—Ni—Co alloy (kovar (trademark)) and formed to have, for example, a cylindrical shape. A through hole (not shown) piercing from the front end face 11a to the rear end face 11b is formed inside the ferrule 11. The optical fiber 3 is inserted into this through hole and fastened by, for example, soldering.
As shown in FIGS. 8 and 9, the fastening members 17 are composed of a pair of fastening parts 10a and 10b (10a′ and 10b′) arranged and fastened on the base part 15 with a space therebetween. The fastening members 17 are fastened to the base 6, for example, at the positions Q by laser welding (for example, YAG laser welding).
At a front side part near the semiconductor laser element 2 and at a rear side part far from the semiconductor laser element 2, the side face of the ferrule 11 is sandwiched from both sides by the pair of the fastening parts 10 (10a, 10b, 10a′, and 10b′) of the fastening members 17. Then, the ferrule 11 is fastened to the fastening parts 10 (10a, 10b, 10a′, and 10b′) by laser welding (for example, YAG laser welding).
To enhance a coupling efficiency, the center of the semiconductor laser element 2 and the center of the optical fiber 3 are adjusted to agree with each other as much as possible. However, in the case of such a structure in which the fastening part is fastened by laser welding, a part to be joined is locally heated and this brings about the situation where the position of the ferrule 11 is displaced with respect to the semiconductor laser element 2 due to melting or solidification contraction of metal. Therefore, there is a manufacturing method in which, before laser welding, the aligning position of the ferrule 11 is displaced in advance by the amount that the ferrule 11 is to be displaced by welding and then the ferrule 11 is returned to the aligning position after welding (see, for example, Patent Document 1).